Diazabicycloalkenes are known and have found use as a catalyst in the preparation of polyurethanes and use in producing various industrial chemicals. For example, ammonia has been reacted with ethylene dichloride in the presence of a diazabicycloalkene to produce ethyleneimine; mononitrobenzene can be reacted with hydrogen in the presence of diazabicycloundecene to form aniline.
Processes for preparing diazabicycloalkenes typically involve three steps, the first comprising the reaction of an unsaturated nitrile with a lactam to produce a cyanoethyl lactam; the second comprising the hydrogenation of the cyanoalkyl lactam in the presence of a hydrogenation catalyst and ammonia to produce an N-(amino-alkyl)-lactam and the third step comprising the cyclic dehydration of the N-(amino-alkyl)-lactam to produce the diazabicycloalkene. The following patents illustrate the preparation of diazabicycloalkenes and particularly 1,8-diazabicyclo[5.4.0]undecene-7 which is commonly referred to as DBU.
U.S. Pat. No. 3,761,436 discloses the preparation of diazabicycloalkenes from N-(amino-alkyl)-lactams and focuses on the third step in the process i.e., the cyclization and dehydration of the N-(amino-alkyl)-lactam to form the diazabicycloalkene. The patentees point out that the reaction conventionally was carried out in the presence of an acid such as phosphoric or hydrochloric acid and noted that addition salts were formed with the bicyclic compounds formed in the dehydration. The resulting acid addition salts which were formed had a tendency to concentrate in the distillation still and resulted in yield loss if not removed. Dehydration and cyclization is accomplished by carrying out the reaction in the presence of an oxide of tin or antimony and a water-immiscible solvent such as toluene or xylene.
Japanese Patent 42-19793 discloses a process for preparing DBU and discusses the three step procedure of cyanoethylating caprolactam followed by reduction and dehydration. The patentees noted that the cyanoethylation of 2-pyrrolidone to produce 1,5-diaza-bicyclo(4.3.0)nonene-5 (DBN) was known and that DBU could be prepared by the cyanoethylation of .epsilon.-caprolactam by reacting with acrylonitrile. DBU was preferred to DBN because it was substantially more active in urethane catalysis than DBN. The patentees point out that the cyanoethylation of the lactam should be carried out in the presence of a basic catalyst such as sodium metal, alkali metal, hydroxides, alkali metal salts, alcoholates and amines. Hydrogenation of the cyanoethyl lactam produced is carried out using a hydrogenation catalyst e.g. Raney nickel in an inert solvent such as a lower alkanol. The dehydration and cyclization of the aminopropyl lactam is performed at temperatures below 300.degree. C. in organic solvents such as toluene and xylene and mixed with modest levels of acid e.g., phosphoric or sulfuric acid.
British Patent 1,121,924 discloses a process for producing bicyclic amidines by dehydrating an N-(amino-alkyl)-lactam in the presence of a mineral acid at elevated temperatures.